This invention relates to a device for controlling the dimension of a rolling material in a continuous rolling machine.
In order to minimize dimensional variations, a conventional continuous rolling machine is provided with a tension control device as shown in FIG. 1.
In the figure, reference numeral 1 designates the an (i-1)th mill stand roll, 2 an i-th mill stand roll, 3 a rolling material, 4 an electric motor for driving each of the rolls, 5 power converters for supplying electric power to the motor, 6 speed control devices, 7 pilot generators for detecting the speeds of the motors, 8 adders for setting speeds for the driving motors 4 in each of the mill stands, 9 rolling pressure detectors, 10 a motor current detector, and 11 a tension control device which comprises a tension detecting device 11a, a comparator 11b for comparing a set tension value with an acutally measured value and a controlling calculator 11c for correcting the speed of the motor 4 according to a tension deviation value.
The operation of this device will now be described. When the tension control device 11 is not in operation, the driver motors 4 are so controlled by the speed controller 6 that their speeds are equal to set values N.sub.i-1 and N.sub.i. The tension control device 11 calculates a tension value t.sub.i,i-1 between the (i-1)th mill stand and the i-th mill stand with the aid of the rolling pressure detection 9 and the motor current detector 10, to thereby correct the speed of the i-th mill stand roll 2 so that the values thus calculated become set values T.sub.i,i-1. The operation of the tension control device 11 is as follows. When the front end of the rolling material 3 is gripped by the (i-1)th mill stand 1, the rolling pressure P.sub.i-1,0 and motor current I.sub.i-1,0 are measured, and a torque arm constant is calculated as: ##EQU1## When the front end of the rolling materal 3 is then gripped by the i-th mill stand 2, the rolling pressure P.sub.i-1 and motor current I.sub.i-1 are measured, and a current variation .DELTA.I which is caused by the tension between the stands is calculated as: EQU .DELTA.I=I.sub.i-1 -C.sub.i-1 .times.P.sub.i-1 ( 2)
As the current variation .DELTA.I due to the tension is proportional to the tension value t.sub.i,i-1, the following calculation can be made: EQU t.sub.i,i-1 =a.sub.i-1 .times..DELTA.I.sub.i-1 ( 3)
The above described calculation of expressions (1), (2) and (3) are made by the tension control device 11a. The difference between the actually measured tension values t.sub.i,i-1 and the set tension values T.sub.i,i-1 is calculated by the comparator 11b, and the amount of speed correction for the i-th mill stand 2 is calculated by the controlling calculator 11c so that the difference signal becomes zero, and is then applied to the adder 8. The rolling material 3 can be maintained under a constant tension as described above.
With the conventional tension control device for the continuous rolling machine constructed as described above, the tension can be constantly maintained at the set value, but the device suffers from a difficulty in that dimensional change due to temperature variations of the rolling material 3 cannot be eliminated. The reason for this is that, when the rolling material 3 is rolled by a hole roll, the width is changed by the tension and is simultaneously changed by the variation in deformation resistance attributable to the variation in temperature of the rolling material.
The foregoing will be described with reference to FIGS. 2 through 5 for a rolling machine having a hole roll as an example. FIG. 2(a) and FIG. 2(b) show sections of a rolling material between mill stands in a continuous rolling machine. More specifically, FIG. 2(a) shows a section between the (i-1)th mill stand and the i-th mill stand, and FIG. 2(b) shows a section after the i-th mill stand. FIG. 3 shows sections of the rolls 2 and the rolling material 3 at the i-th mill stand. The width B of the rolling material 3 is changed by the tension (compressive force) between the mill stands because it is not regulated by the rolling rolls 2.
FIG. 4 indicates the relationship between tensions (compressive forces) between the stands and width variations .DELTA.B. As is clear from FIG. 4, as the tension increases, the width variation is increased negatively, and as the compressive force increases, the width variation .DELTA.B is increased positively. As the deformation resistance of the rolling material 3 is decreased, the relation of the width variation .DELTA.B to the tension (compressive force) is increased. FIG. 5 shows the relationship between the temperature and the deformation resistance in the rolling material. As the rolling material temperature increases, the deformation resistance is decreased.
Because of the relationships described above, as the rolling material temperature changes with the tension maintained at a constant value, the deformation resistance is changed also. As the temperature is decreased as in the case of a skid mark, the deformation resistance is increased, and the width of the rolling material 3 is changed from the point A to the point B indicated in FIG. 4.